Electroluminescent materials that are based on nanocrystals of J-aggregates in semiconductor polymer mediums, such as aromatic polyimides, polyvinylcarbazole, and derivatives of polyphenylenevinylene, are known. When J-aggregate polymer nanocomposites comprising molecular nano-size crystals of cyanine dyes are used as light-emitting layers in organic light-emitting diodes, intensive electroluminescence of a saturated color may be observed. The J-aggregates nanocrystals may be in a three-dimensional or one-dimensional filamentary form, which occupy an intermediate position between microcrystals and individual molecules. A distinctive optical characteristic of J-aggregates is the presence of intensive narrow bands of optical absorption and fluorescence, which are positioned in the range from blue to the near IR-region of the spectrum depending on the structure of the molecules of cyanine dyes. Due to their small size, the polymer nanocomposites do not scatter light in thin layers that remain optically transparent even with a large content of the nanophase. None of the known types of electroluminescent nanocomposite materials have such optoelectronic properties. The J-aggregate-based materials combine optical characteristics typical for organic molecular crystals as well as the physicomechanical and current conducting properties of polymer semiconductors.
The formation of known polymer electroluminescent layers may be prepared as follows. A polymer and a cyanine dye may be dissolved in a nonpolar organic solvent which may comprise chlorine atoms in tetrachloroethane. Then, the solution may be spin-coated onto a conducting substrate, such as a glass plate coated with a transparent electroconductive film of tin and indium tin oxides (ITO), and the solvent may be evaporated to form a solid film. The formation of J-aggregates occurs in the liquid solution of the dye and the polymer in the organic solvent.
A disadvantage of the known J-aggregate polymer nanocomposites is the extreme limitation in selection of initial molecule structures of cyanine dyes for the formation of the nanocrystalline phase. This is due to poor solubility of salt-like compounds, such as cyanine dyes in nonpolar organic solvents. Additionally, even in the case of relatively well-dissolved cyanine dyes, the formation of J-aggregates is difficult, since the probability of formation of J-aggregates from a monomolecular form is greatly reduced upon transition from polar to nonpolar solvents. A property characteristic for cyanine dyes is the effective formation of nanocrystals of J-aggregates in water and aqueous solutions. However, the necessity to use nonpolar organic solvents is related to the insolubility of known polymers with electron-hole transport in polar solvents. In addition, the dyes may not provide a stable thermoresistant nanophase of J-aggregates and a wide range of electroluminescence characteristics.